The proposed research will investigate the relationship between handedness, direction and extent of hemispheric lateralization of function, and performance on spatial-cognitive tasks in older adults (age 60-72) and young adults (age 18-30). This line of research was derived from one of the paradoxes of gerontological research, namely that older adults consistently show a greater deficit in so-called "right hemispheric" functions (e.g., spatial abilities) than in "left hemispheric" functions (e.g., verbal abilities), yet the neurobiological changes in the brain which presumably underly or contribute to this deficit show no apparent hemispheric asymmetry. One possible explanation is that right hemispheric functions are more diffusely organized and thus more susceptible to generalized decline in efficiency. If this is true, then individuals exhibiting an even greater diffuseness of representation of spatial functions across both hemispheres should show a greater age-related decline. The prposed research will test this hypothesis. The direction and degree of hemispheric lateralization of function will be assessed by comparing performance in identifying verbal and visuospatial materials tachistoscopically presented to the left or right visual half-fields of right and left handed subjects. On the basis of these performance scores subjects will be assigned to one of three groups: spatial abilities strongly right-lateralized, strongly left-lateralized, or weakly (or ambiguously) lateralized. The performance of these three groups will then be assessed on a perceptuo-motor spatial task (Block Design) and a visuo-cognitive spatial task (Mental Rotation). Analyses of variance will be used to test the hypothesis that those older individuals exhibiting the least lateralization (i.e., the greatest diffuseness of representation) of spatial tasks, relative to the performance of the younger adults.